U.S. airlines lost their fight last week to stay out of the European Union’s carbon trading market at the E.U.’s highest court.

The Court of Justice of the European Union in Luxembourg ruled in a lawsuit brought by the Air Transport Association of America, American Airlines and United Continental that aviation can be included in the E.U.’s emissions trading system (ETS). The decision cannot be appealed.

“The directive including aviation activities in the E.U.’s emissions trading scheme is valid,” the court said in a statement. “Application of the emissions trading scheme to aviation infringes neither the principles of customary international law at issue nor the open-skies agreement.”